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Subject: Re: Why kinfo_getvmmap is sometimes so expensive?
To: Konstantin Belousov <kostikbel@gmail.com>
References: <e6dc27c0-0454-0666-b3e1-887bd116a847@rawbw.com>
 <20160707001913.GJ38613@kib.kiev.ua>
Cc: Freebsd hackers list <freebsd-hackers@freebsd.org>
From: Yuri <yuri@rawbw.com>
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Date: Wed, 6 Jul 2016 18:55:56 -0700
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On 07/06/2016 17:19, Konstantin Belousov wrote:
> To calculate residency count for the process map entries, kernel has to
> iterate over all pages.  This operation was somewhat optimized in 10.3
> and HEAD, particularly for the large sparce mappings.  But for large populated
> mappings there is no other way then to check each page.
>
> You may confirm my hypothesis by setting sysctl
> kern.proc_vmmap_skip_resident_count to 0 and see whether the CPU
> consumption changed.  Of course, you will not get the resident count
> in the returned structure, after the knob is tweaked.


Yes, this explains it. kern.proc_vmmap_skip_resident_count=0 made CPU 
consumption to go down.

So, it is better to parse /proc/<pid>/map to get the process size.


Thank you,

Yuri